i think you will find that this is normal behavior, mine does it all the time. if you notice when you clean the inside glass he will point head down at me to expose his spines at me like for his protection. i think i got a pic i'll post.
No them cruising all the time would be a bad sign. The only time any of mine have done active swimming is when they think I have not fed them enough. When that are upside down in a corner or by a rock is natural. I kinda like it. As long as the fish is happy so am I. Just always check were he is when scrubbing algae. Or you too will learn a very painful lesson. YEEOOUCH !